In an information-oriented society in recent years, the system using radio, such as mobile communications and satellite communications, has spread quickly. Along with that, more miniaturization has been required of communications systems in addition to high performance and high efficiency. The size of communications systems is highly dependent on the size of an antenna. Therefore, in order to miniaturize communications systems, it becomes important to miniaturize an antenna, without lowering its performance.
A sufficiently small antenna, as compared with the wavelength of the radio signal used in communications systems, is called a miniaturized antenna. Various design methods have been proposed as a miniaturized antenna (for example, refer to Patent Literature 1, Patent Literature 2, and Non Patent Literature 1).    [Patent Literature 1]: JP 2004-274513 A    [Patent Literature 2]: JP 2003-283211 A    [Non Patent Literature 1]: Yoko Koga, et al., “Design and Evaluation of Miniaturized HTS Slot Array Antenna with Bandpass Filter”, the technical report of the proceeding of the Institute of Electronics, Information and Communication Engineers (SCE2002-5, MW2002-5), 2002, p.23-28